The 5-year survival rate for Pancreatic ductal adenocarcinoma (PDAC) patients is about 5% and has remained largely unchanged over the past 25 years. It is imperative that the mechanisms that underlie this cancer be rapidly identified and investigated so that novel molecular therapies can be developed. For the most part, the signaling mechanisms deregulated in response to genetic alterations in the Ki-Ras gene, and by other well- established hallmarks of pancreatic carcinogenesis, are still incompletely understood. The long-term goal is to elucidate the role and regulation of the phosphoinositide 3-kinase (PI3K) signaling pathway and its protein ki- nase mediator Akt in PDAC and develop more effective antagonists against them for cancer prevention and therapy than are currently available. In pursuit of this goal, a modified yeast two-hybrid screen with Akt as bait helped identify BSTA as a previously unknown mediator of PI3K/Akt signaling. The objective of this proposal is to further understand BSTA regulation and function and the effects of blocking its activity on PDAC. The central hypothesis is that BSTA is a key regulator of oncogenic Ki-Ras-induced Akt signaling and promotes pancreatic tumorigenesis. Based on strong preliminary data, this hypothesis will be tested by pursuing the fol- lowing two specific aims: 1) Identify the mechanism by which Ki-Ras activates Akt; and 2) Investigate the role of BSTA in the resistance of PDAC to mTOR inhibitors in vitro and in vivo. An RNAi-based approach, and pro- tein phosphorylation assays, will be used to test the working hypothesis (Aim 1) that oncogenic Ki-Ras acti- vates Akt in PDAC cells by a) increasing BSTA expression via a mechanism involving the Ral small GTPases and microRNA miR-21, and b) stimulating Akt kinase (mTORC2) and/or suppressing Akt phosphatase (PHLPP) in a BSTA-dependent mechanism. To test if BSTA promotes pancreatic tumorigenesis and drug re- sistance (Aim 2), the minimal Akt-binding sequence on BSTA will be delineated and cell-penetrable peptides designed to test on PDAC cells. BSTA will be also be downregulated in PDAC cells to investigate tumorigene- sis and resistance to mTOR inhibitors in an orthotopic mouse model. The rationale for the proposed project is that understanding the role and regulation of BSTA may help identify novel ways to target the PI3K pathway and oncogenic Ki-Ras signaling for the effective treatment of PDAC. This contribution is significant because it is expected to help reveal details of a novel mechanism by which K-RasG12D additionally controls Akt and lead to the development of alternative pharmacologic strategies for targeting the PI3K/Akt pathway in pancrea- tic ductal cancer. The research proposal is innovative because it describes a novel mechanistic link between oncogenic Ki-Ras and Akt that will, once properly delineated, offer a new and substantially different approach for targeting the PI3K/Akt pathway than currently available. Together, these studies are expected to have a positive impact by fundamentally advancing the understanding of Ki-Ras and PI3K/Akt signaling and uncover new molecular targets for the treatment of pancreatic ductal cancer. PUBLIC HEALTH RELEVANCE: Pancreatic cancer is a highly aggressive and rapidly fatal disease. The studies proposed in this grant application may be expected to fundamentally advance our understanding of Ki-Ras and PI3K/Akt signaling and uncover new molecular targets and alternative therapeutic strategies for the treatment of pancreatic ductal cancer. The proposed research is therefore relevant to public health and to the NIH mission as defined in the Consensus Report of the NCI Clinical Trials Planning Meeting on Pancreas Cancer Treatment.